An enhanced ground proximity warning system (EGPWS) monitors a threat in front of an aircraft. In cases where the aircraft experiences an altitude error, the aircraft could crash into terrain without any EGPWS generated alerts. This problem arises especially when the EGPWS is installed in aircraft that operates very close to the ground, such as helicopters. Therefore, there exists a need for a system that would provide consistent and reliable EGPWS alerts in such an environment, thereby enhancing aircraft safety.
An improved aircraft terrain avoidance system, method and computer program product that reduces nuisance alarms is provided. The system includes a geometric altitude component, first and second vertical safety margin generators, and an alert component. The geometric altitude component generates a geometric altitude vertical error value based on barometric altitude and a positioning system value, such as a global positioning system generated value. The first vertical safety margin generator generates a first vertical safety margin value based on the generated vertical error value and safety margin limits. The second vertical safety margin generator generates a second vertical safety margin value based on the generated first vertical safety margin value, aircraft groundspeed, and aircraft distance to a selected runway. The alert component outputs an alert signal to the flight crew if it determines an alert condition exists based on the generated vertical safety margin.
In accordance with further aspects of the invention, the second vertical safety margin generator includes a groundspeed-based generator, a distance-from-runway-based generator, and a selector. The groundspeed-based generator generates a groundspeed safety margin value based on the first safety margin value, aircraft speed, and a predefined hover and approach speed. The distance-from-runway-based generator generates a distance-from-runway safety margin value based on the first safety margin value, a predefined runway distance bias, and aircraft distance to a selected runway. The selector makes the lesser of the groundspeed safety margin value and distance-from-runway safety margin value the second vertical safety margin value.
In accordance with other aspects of the invention, the system further includes a terrain floor generator that generates a terrain floor height value based on aircraft groundspeed, a predefined hover speed and approach speed, and a runway distance based terrain floor height value. The alert component further outputs an alert signal to the flight crew if an alert condition exists based on the generated terrain floor height value.
As will be readily appreciated from the foregoing summary, the invention provides a ground avoidance system that takes into consideration an altitude error value, and an aircraft""s speed and position relative to an airport when determining how to evaluate threats.